When the team’s only 10-game winner took the mound Friday night at Fenway Park, there was every expectation the 24-year-old lefthander would help the Sox prevent a two-game skid from becoming a three-game slide.

That, however, was not the case. Doubront was unable to hold a 5-1 lead the Sox had given him with a four-run fourth inning. He squandered that by slowly unraveling on the mound, allowing his frustrations with plate umpire Mark Wegman’s strike zone to get the best of him in a four-run fifth by the Twins.

“It was a roaming strike zone tonight,’’ said Sox manager Bobby Valentine said after the 6-5 loss in 10 innings. “”But his ball was really moving.’’

Doubront did not factor in the outcome to remain winless over his last three starts, a stretch in which he has allowed 12 runs (nine earned) on 20 hits and 8 walks over 16⅓ innings.

But it was the fifth inning, his last of the game, that upset him most.

With one out, Doubront loaded the bases, allowing a fielder’s choice to Denard Span, a single to left by Ben Revere, and a walk to Joe Mauer on a 3-and-2 fastball that just missed.

It prompted a mound visit from pitching coach Bob McClure, but it seemed to help little when Doubront walked Josh Willingham, which allowed Span to score to make it 5-2.

“I’m not sure he had trouble commanding his fastball, but it was right around the zone,’’ said catcher Kelly Shoppach. “He just couldn’t get ahead of guys and it ended up costing him.’’

When Doubront ran the count to 2-and-1 to the next batter, Justin Morneau, it prompted a mound visit from second baseman Dustin Pedroia.

“He just told me to stay calm,’’ Doubront said. “I told him my pitch was close enough for [Wegman] to call it a strike and I just got a little bit frustrated when those calls were close to the strike zone.’’

Little good it seemed to do him, though, when Morneau slapped a two-run single to shallow center that flew over Pedroia’s head.

“That fifth inning, the bloop upset him a little. That two-strike hit upset him,’’ Valentine said. “A couple of pitches upset him. He had Morneau two strikes and he hit it off the end of the bat. He just missed making that pitch to get him out of the inning, which he’s been making all year.’’

But not Friday night.

“When I didn’t get those calls, I started to throw those balls up in the zone and committing mistakes,’’ Doubront said. “I just tried to keep the ball down and not let what happened happen.’’